There's only so much energy you can get out of a gallon of various fuels. I've read about those so-called 100 mpg carburators - and am skeptical of the veracity of the claims. The auto industry has no more desire to throw away money than any other industry.

I remember some of their first efforts at higher-mileage cars, and they sucked dead bunnies. It wasn't just engine performance, it was total quality and general crap. It's going to take me quite a bit of convincing that they pushed that suckage out the door if a carburator would have given them 100 mpg. At least they'd have had high-mileage suckage. And it's hard for me to believe that Toyota and Honda and BMW and even the Yugo wouldn't have cleaned their clock in any way and every way they could have.